Cracks, shifting slopes and altered watercourses in Longleng raise fears of prolonged ground instability after devastating July monsoon landslides
DIMAPUR — The monsoon landslides that devastated parts of Longleng and Mon districts in July have left residents in and around Tamlu grappling with a new concern: whether the ground itself is becoming unstable.
Residents have reported cracks in houses and roads, shifting slopes and changes in the course of water following the heavy rains and landslides. The July 19 disaster killed eight people in one major slope collapse, with six bodies recovered and two still missing, according to local accounts cited in a recent ground report.
The extent of the damage has left many residents worried that the problem may not end with the monsoon.
In Tamlu, sections of roads were badly damaged and cracks appeared in several houses after the ground shifted. Some slopes have reportedly moved downhill, raising concerns about further movement during another spell of heavy rain.
The damage has also been reported beyond Tamlu. Longleng Deputy Commissioner W Manpai Phom told Down To Earth that every village in the district had suffered damage, with several villages cut off for days after roads collapsed or were blocked.
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In some areas, residents say the landscape itself has changed. Streams have reportedly disappeared or changed course, while new ponds have appeared around Tamlu and Yongnyah. One local account estimated that some of the new water bodies could be around 50 feet deep.
The changes have inevitably brought back memories of prolonged ground movement in parts of Noklak and Tuensang.
Noklak has been dealing with a slow-moving landslide for decades. What began as a relatively small slide in 1980 had affected nearly a quarter of the town by 2022, with some areas continuing to sink. Tuensang, too, has seen the gradual expansion of a landslide that began in Phinjang colony in the late 1990s.
Geologists, however, have cautioned against drawing a direct parallel between those cases and the recent events in Tamlu and Mon without further investigation.
Temsulemba Walling, senior geologist and professor at Nagaland University, said that the July 19 landslides in Tamlu and Mon were most likely triggered by heavy rainfall acting on steep slopes with unfavourable geological and drainage conditions.
The geological setting also differs from that of Noklak, he pointed out. The Tamlu slide occurred in Disang shales, while the Mon landslide was in the Laisong Formation of the Barail Group.
Gauhati University geologist Sarat Phukan similarly attributed the Tamlu movement primarily to rainfall. He said the area had received substantial rain in the week before July 19, followed by heavy rainfall on July 18 and 19.
The accumulated moisture would have raised groundwater levels and weakened the slope material, while intense rainfall increased pore-water pressure, making the slopes more susceptible to failure, he explained.
Phukan, however, cautioned that further movement could occur during future periods of prolonged or heavy rainfall. At the same time, he said there was not enough information to determine the likely depth or size of any future movement, or how likely it was to occur.
The role of human activity is another question that remains open. Road construction, hill cutting, blasting and changes to drainage have been cited as possible factors in the affected areas. Coal mining along the Dikhu has also come under scrutiny.
Experts, however, say that such links need to be established through scientific investigation rather than assumed.
According to Walling, there was currently insufficient evidence to directly connect coal mining with the recent disruption of the Dikhu. Establishing such a link, he said, would require analysis of satellite data from different periods.
There is also no evidence so far that an earthquake triggered the July movement. Phukan said that earthquakes recorded in the region around July 17 and 18 were too small, distant and deep to account for the damage. A very small local earthquake, however, could not be completely ruled out in the absence of nearby seismic stations.
For residents, the scientific questions offer little immediate comfort. Their more pressing concern is what will happen when the next prolonged spell of rain arrives.
With houses already showing cracks, roads damaged and watercourses altered, communities in Tamlu and surrounding areas are watching the slopes and waiting for a detailed assessment of the ground conditions.
Whether the July disaster was an extreme consequence of heavy rainfall or a sign of longer-term ground instability remains unclear. For residents living with the cracks, that uncertainty is itself a source of fear.
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